1. Field of the Invention
The present invention relates to panel sensing device and a positioning location searching method of the same, in which phase difference is used to determine a touch position of a sensing pen on a sensing plate.
2. Description of the Related Art
In general, an electronic book has a sensing pen and a plurality of sensing pages. The sensing pen is used to touch the sensing pages for selecting desired items. FIG. 1 schematically illustrates a sensing plate of a conventional electronic book 11, wherein two ends A1 and B1 are inputted with driving waveforms for getting the row position of the sensing pen 12. The other two ends C1 and D1 are applied with driving waveforms for getting the column position of the sensing pen 12.
FIG. 2 shows the driving waveforms applied to the four ends A1, B1, C1 and D1. At Initial time, for example 10 to 20 micro seconds, the four ends are applied with identical reference voltage waveforms. Then, at about 6˜9 seconds, an addressing voltage waveform (row) is applied to the A1 end so that the sensing pen 12 can sense an electric field waveform, as shown in FIG. 3, by sensing the electric field.
Because the distribution of the electric field is linear, it is able to determine the current touching position of the sensing pen 12 via comparing the voltage that the sensing pen 12 detected in the addressing voltage waveform period (i.e., 6˜9 seconds) with the voltage that the sensing pen 12 detected in the reference voltage waveform period (i.e., 0˜3 seconds).
However, the sensing pen 12 needs to use a high precision analog to digital converter to sense the strength of amplitude. If a high resolution is required, a highly precise analog to digital converter is required, resulting in the increase of the manufacturing cost. Moreover, the amplitude and energy caused by sensing voltage are difficult to control to get a good precision and to match the specification in mass production.